Method and layout of an integrated circuit

ABSTRACT

A method of designing a layout includes identifying a cell having a cell height being a non-integral multiple of a minimum pitch, generating, using a processor, possibilities of an ordered arrangement of a plurality of virtual grid lines parallel to the top boundary and the bottom boundary, and placing at least two conductive patterns on the plurality of virtual grid lines. The cell height is defined by a top boundary and a bottom boundary, and the minimum pitch is based on a manufacturing process. The plurality of virtual grid lines are separated from each other by a plurality of spacings, and the top boundary overlaps a first virtual grid line of the plurality of virtual grid lines and the bottom boundary overlaps a second virtual grid line of the plurality of virtual grid lines. At least one spacing is different from another spacing of the plurality of spacings.

BACKGROUND

In a design of an integrated circuit, various cells having predeterminedfunctions are used. Pre-designed layouts of standard cells or memorycells are stored in cell libraries. During the integrated circuit designprocess, the pre-designed layouts of the standard cells are retrievedfrom the cell libraries and placed at selected locations in anintegrated circuit layout. Routing is then performed to connectcomponents of the standard cells with each other using interconnectlines. Next, an optical proximity correction (OPC) is performed and aset of masks are generated to manufacture the integrated circuit usingsemiconductor manufacturing processes.

Because of the complexity of various designs, an electronic designautomation (EDA) tool is used to simulate and verify the integratedcircuits at various levels of abstraction under the direction of adesigner, in some instances. From design to mask fabrication, the EDAtool performs various tasks, such as design rule checking, layout versusschematic checking, layout parasitic extraction andresistance-capacitance (RC) extraction.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a top view of a layout of a cell in an integrated circuit inaccordance with some embodiments.

FIG. 2A is a flow chart of a method of designing an integrated circuitlayout in accordance with some embodiments.

FIG. 2B is a flow chart of a method of adjusting virtual grid lines inaccordance with some embodiments.

FIG. 3 is a table of a predetermined number of pitch options inaccordance with some embodiments.

FIG. 4 is a top view of a layout of a cell in an integrated circuit inaccordance with some embodiments.

FIG. 5 is a top view of a layout of a plurality of cells in anintegrated circuit in accordance with some embodiments.

FIG. 6 is a functional block diagram of an integrated circuit designingsystem in accordance with one or more embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components, values, operations, materials,arrangements, or the like, are described below to simplify the presentdisclosure. These are, of course, merely examples and are not intendedto be limiting. Other components, values, operations, materials,arrangements, or the like, are contemplated. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

An integrated circuit includes, in some instances, a memory cell arrayand/or standard cells. The memory cell array includes a plurality ofmemory cells arranged in rows and columns. In some embodiments, a memorycell includes a transistor-based bi-stable latch that is either in an‘on’ state or an ‘off’ state. The memory cells in each column arecoupled to at least one bit line for writing data to or reading datafrom the memory cells. The memory cells in each row are coupled to aword line for selecting a writing or reading operation. In someembodiments, the memory cell array includes one or more control linesextending along one or more columns or rows for controlling differentoperations of the memory cells.

Standard cells include functional cells and non-functional cells, i.e.,engineering change order (ECO) cells, for various applications. Afunctional cell is designed to perform a specific function such as alogic function or a storage function. An ECO cell is designed without aspecific function, but is programmable to provide a specific function.During an integrated circuit design, designed layouts of one or morefunctional cells are read out from cell libraries and are placed into aninitial layout. In some embodiments, neighboring cells are abutted toeach other.

A place and route electronic design automation (EDA) tool is used togenerate the initial layout for a mask to be used to form one or morecircuit patterns of a semiconductor device. During the operation of theEDA tool, one or more virtual grid lines are arranged in parallel witheach other in the standard cell. The virtual grid lines extend across anentirety of the layout which includes the standard cell. The virtualgrid lines in neighboring cells are continuous. Routing is performed toconnect the functional cells by using one or more interconnect patternsplaced on the virtual grid lines. Each pattern extends along a singlevirtual grid line. The layout also includes one or more ECO cellsdisconnected from the functional cells. When the layout is revisedbecause of a functional violation or a timing violation, one or more ECOcells are programed to provide an intended function and are connected tothe functional cells by one or more interconnect patterns placed on thevirtual grid lines. As a result, the design cycle time is shortened andmask changes are reduced in comparison with other approaches.

In some embodiments, the interconnect patterns in abutted standard cellsare symmetric along a cell height direction. In some embodiments, aplurality of spacings between adjacent virtual grid lines in thestandard cell is symmetric along the cell height direction. At least onespacing of the plurality of spacings is different from another spacingof the plurality of spacings in the standard cell. As a result of thesymmetry, the cost and time of designing the layout and/or manufacturingthe integrated circuit (IC) are reduced, and a density of the IC isincreased. In at least one embodiment, the interconnect patternscorrespond to conductive lines or via plugs in a semiconductormanufacturing process.

FIG. 1 is a top view of a layout 100A of a cell 110 in an integratedcircuit in accordance with some embodiments. In some embodiments, cell110 is a standard cell. Cell 110 includes, but is not limited to, anINV, AND, OR, NAND, NOR, XOR, AOI, OAI, MUX, BUFF, adder, filler,flip-flop, latch, delay, clock cell, or the like. Layout 100A has aplurality of virtual grid lines GL11-GL18, collectively referred to asvirtual grid lines GL, extending in a direction X and cell 110 has acell height CH along a direction Y perpendicular to direction X. Cell110 includes a top boundary 120T and a bottom boundary 120B. Cell heightCH is defined as a distance from top boundary 120T to bottom boundary120B. Virtual grid lines GL, also referred to as routing tracks, arespaced from each other along cell height CH from top boundary 120T tobottom boundary 120B and are used for facilitating the placement androuting process in which conductive patterns are placed forinterconnecting components of the layout. In some embodiments, directionY is parallel with a longitudinal axis of gate structures of the IC. Insome embodiments, direction Y is perpendicular to the longitudinal axisof gate structures of the IC.

In some embodiments, cell 110 is used in asingle-height-cells-in-single-row layout design. In the layout design ofsingle-height cells, a plurality of cells with the same cell height CHare abutted and arranged in a row, and the virtual grid lines in eachcell are consecutive and in parallel with each other. The row extendsalong direction X. In some embodiments, according to the complexity ofthe integrated circuits, in a single-height-cells-in-single-row layoutdesign, one or more rows are arranged in a two-dimensional (2-D) array.In some embodiments, cell 110 is used in amixed-height-cells-in-single-row layout design. In the layout design ofmixed-height cells, a plurality of cells with different cell heights areabutted and arranged in a row. Each cell height is an integral multipleof standard cell height CH. Still, the virtual grid lines in eachabutted cells are consecutive and in parallel with each other. Comparedwith the single-height-cells-in single-row layout design, themulti-height-cells-in-single-row layout design has a more efficient areause.

In some embodiments, cell 110 has an even number of virtual grid linesGL extending in parallel with each other and extending along direction Xand an odd number of spacings S1112-1718, collectively referred to asspacings S, between adjacent virtual grid lines GL. In some embodiments,cell 110 includes an odd number of virtual grid lines GL and an evennumber of spacings S. FIG. 4 includes an example of a cell having an oddnumber of virtual grid lines GL and an even number of spacings S.Virtual grid lines GL extend through an entirety of the layout design.In the EDA tool, conductive patterns are arranged (also known asplacing-and-routing) along virtual grid lines GL. Because cell height CHis a non-integral multiple of a minimum pitch MP of a predeterminedmanufacturing process, when spacings S are uniform, at least one ofvirtual grid line GL11 or GL18 will fail to align with boundaries, e.g.,top boundary 120T or bottom boundary 120B, of cell 110. As a result, arisk of violating the design rule of minimum pitch MP at a locationwhere two neighboring cells abut is increased. In addition,inconsistency and difficulty of pattern coloring are increased. In orderto help ensure that virtual grid line GL11 is aligned with top boundary120T and that GL18 is aligned with bottom boundary 120B, a magnitude ofeach of spacings S is arranged in a way that at least one of spacings Sis different from at least another of spacings S. This adjustment to thespacings S accounts for the non-integral multiple relationship betweencell height CH and minimum pitch MP. In some embodiments where spacingsS were previously set to be equal to minimum pitch MP, at least onespacing of spacings S is increased.

FIG. 2A is a flow chart of a method 200A of designing an integratedcircuit layout in accordance with some embodiments. One of ordinaryskill in the art would understand that additional operations are able tobe performed before, during, and/or after method 200A depicted in FIG.2A, in some embodiments. Method 200A includes operation 210 in which alayout of a standard cell having a cell height in a first direction isreceived. A hardware computer receives the layout of the standard cell.In some embodiments, the layout is received from a layout generator, auser or another suitable external device. In some embodiments, thelayout is generated using a same system as that which executes method200A. The layout is usable to manufacture an integrated circuit by usinga manufacturing process and the layout is designed based on a set ofdesign rules in various layers such as well regions, active regions,polysilicon structures, contact plugs, conductive lines, vias, or thelike. The set of design rules of the predetermined manufacturing processhas a minimum pitch which is used to determine a minimum distancebetween edges of patterns disposed end-to-end, a minimum distancebetween parallel adjacent patterns, and/or a minimum distance betweencorners of adjacent patterns.

Method 200A continues with operation 220 in which a spacing betweenadjacent virtual grid lines is adjusted. In some embodiments, becausethe cell height is determined based on various manufacturing processesof each layer and area use, the cell height may be a non-integralmultiple of the minimum pitch. When the virtual grid lines are arrangedaccording to the minimum pitch, patterns will be asymmetric to eachother every two rows, in some instances. The spacing between adjacentvirtual grid lines is adjusted to satisfy the minimum pitch of thepredetermined manufacturing process and to align a first virtual gridline with a top boundary of the cell and a second virtual grid line witha bottom boundary of the cell. In accordance with such spacing, patternswill be symmetric to each other every two rows.

FIG. 2B is a flow chart of a method 200B of adjusting virtual grid linesin accordance with some embodiments. One of ordinary skill in the artwould understand that additional operations are able to be performedbefore, during, and/or after method 200B depicted in FIG. 2B, in someembodiments. Because spacing is determined by a minimum pitch MP, method200B includes operation 221 in which the cell height is divided byminimum pitch MP. The quotient is a mixed number because cell height isa non-integral multiple of the minimum pitch. The whole number L of thequotient is used to determine the quantity of spacings as well asvirtual grid lines.

In some embodiments, a ratio of cell height CH to minimum pitch MP isp/q, and p and q are positive integers. In some embodiments, the ratioranges from about 4 to about 17. If the ratio is too small, a number ofvirtual grid lines available for interconnect patterns will beinsufficient to connect components of the IC layout, in some instances.If the ratio is too great, a drive current for a cell, e.g., cell 110(FIG. 1), will be increased, resulting in a higher power consumption, insome instances.

In some embodiments, minimum pitch MP is determined based on a minimumpitch which is reliably creatable using a lithography process or etchingprocess used for patterning a conductive pattern. Cell height CH isdivided by L spacings. Whole number L is a positive integer equal to orgreater than 4. In some embodiments, whole number L ranges from 4 to 16.In some embodiments, whole number L is greater than 16.

Method 200B continues with operation 222 in which a predetermined numberof pitch options is assigned. In some embodiments, pitch options forspacings between adjacent virtual grid lines are selected based on anarithmetic sequence by adding minimum pitch MP, also referred as to theinitial element, to a predetermined common difference M. In someembodiments, a predetermined number N of pitch options are assigned. Insome embodiments, common difference M and/or number N is provided by auser. In some embodiments, common difference M and/or number N isdetermined based on empirical data. In some embodiments, number N is apositive integer ranging from about 2 to about 5. If number N is toogreat, a process time of the EDA tool will be increased because of anincreased amount of data to be processed, in some instances. If number Nis equal to 1, there will be insufficient solutions to adjust thespacings of the virtual grid lines, in some instances. Common differenceM is a positive integer equal to or greater than 1. In some embodiments,common difference M is determined based on a relationship betweenminimum pitch MP and a cell height. As a result, a magnitude of eachpitch option for the spacings is equal to or greater than minimum pitchMP.

FIG. 3 is a table of the predetermined number of pitch options inaccordance with some embodiments. In some embodiments, common differenceM ranges from 1 to 4. If common difference M is too great, the number ofvirtual grid lines will be reduced, resulting in insufficient routingoptions for interconnection, in some instances. In some embodiments, thearithmetic sequence begins from setting number N as 2 and setting commondifference M as 1. For example, in at least one embodiment, when cellheight CH is 300 nanometers (nm) and minimum pitch MP is 40 nm, assumingpredetermined number N is 3 and common difference M is 2, the pitchoption is selected as {40 nm, 42 nm, 44 nm}.

Method 200B continues with operation 223 in which possibilities of anordered arrangement of the plurality of virtual grid lines are generatedbased on the number N of pitch options and the whole number L.

Because a repetition of N pitch options for L spacings is allowed, thepossibilities of the ordered arrangement of the virtual grid lines isN^(L). Further, because cell height CH is a non-integral multiple ofminimum pitch MP and common difference M is equal to or greater than 1,the possibilities of a uniform spacing are able to be removed.Accordingly, N possibilities are removed so that there are (N^(L)−N)different possibilities. Removing the N possibilities helps to reduceprocessing time for the EDA tool. After the pitch options for spacingsare generated from (N^(L)−N) possibilities of the ordered arrangement ofvirtual grid lines, a size of a solution set is reduced by eliminatingpitch options that fail to meet certain criteria.

Method 200B continues with operation 224 in which a sum of spacings iscompared to the cell height. In order for the virtual grid lines to bealigned with both the top boundary and the bottom boundary of the cell,the sum of the spacings is equal to the cell height. For example, inFIG. 1 to have virtual grid line GL11 align with top boundary 120T andvirtual grid line GL18 align with bottom boundary 120B, a sum ofspacings S equals cell height CH. In some embodiments, because adistance between virtual grid lines GL11 and GL18 defines cell heightCH, possibilities that have a sum of spacings different from cell heightCH are excluded. If the sum of spacings in all possible pitch options isdifferent from cell height CH, method 200B returns to operation 223 anda value of predetermined number N and/or common difference M is changed.If at least one possibility of pitch options has a sum of spacings Sequal to cell height CH, method 200B proceeds to operation 225.

Method 200B continues with operation 225 in which whether the pluralityof virtual grid lines is symmetric along the predetermined direction isdetermined. In the at least one embodiment in FIG. 1, cell 110 has anodd number of spacings, so pairs of spacings S1112/S1718, S1213/S1617and S1314/S1516 are symmetric about a center line of spacing S1415. Ifvirtual grid lines GL are not symmetric to each other along direction Y,method 200B returns to operation 223 and a value of predetermined numberN and/or common difference M is changed. If virtual grid lines GL aresymmetric to each other along direction Y, method 200B proceeds tooperation 226.

Method 200B continues with operation 226 in which whether the orderedarrangement of the plurality of virtual grid lines violates a designrule is determined. In some embodiments, even though a spacing betweentwo adjacent conductive patterns satisfies the minimum pitch MP, due toa limitation of the manufacturing process, the spacing is undesirablewhen the two adjacent conductive patterns are formed using differentmasks. Such violation is also referred to as a forbidden spacing issue,in some instances. Because the arrangement of the plurality of virtualgrid lines should meet all design rules, if a design rule is violated,method 200B returns to operation 223 and a value of predetermined numberN and/or common difference M is changed. If no violation is detected,method 200B permits method 200A to proceed to operation 230. In someembodiments, if all generated possibilities fail to satisfy operation230, the process will stop or an indication of no availablepossibilities will be generated. For example, in at least oneembodiment, when cell height CH is 300 nm and minimum pitch MP is 40 nm,cell height CH is a non-integer multiple (7.5) of minimum pitch MP andwhole number L is 7. Assuming predetermined number N is 4 and commondifference M is 1, one generated possibility satisfying operations224-226 is selected as {43 nm, 43 nm, 43 nm, 42 nm, 43 nm, 43 nm, 43nm}.

In some embodiments, at least one of operations 224-226 is implementedsimultaneously with another of operations 224-226. In some embodiments,operations 224-226 are implemented sequentially, before or after eachother, in various orders. In some embodiments, when more than onepossibility of the ordered arrangement are obtained, the user willselect one possibility based on a different design requirement. Forexample, a possibility with a largest number of virtual grid lines forproviding a maximum number of options to connect components of the IClayout, in some instances.

Returning to FIG. 2A, method 200A continues with operation 230 in whichat least two conductive patterns are arranged on the plurality of gridlines. The arrangement of one or more conductive patterns, also referredto as interconnect structures, includes placement and routing. Theplacement involves deciding where to place the components ofsemiconductor devices of the cell. Routing involves connecting each ofthe placed component with conductive patterns while following the rulesand limitations of the manufacturing/design process. In someembodiments, the placement and routing use a minimum spanning tree (MST)algorithm to find the minimum number of conductive patterns to make aconnection. In some embodiments, the placement and routing use a greedymethod to select the virtual grid lines for each of the conductivepatterns for connecting the semiconductor devices.

In the at least one embodiment in FIG. 1, cell 110 includessemiconductor devices formable using a manufacturing process andincludes conductive patterns (also referred to as polygons) 130 a-d,collectively referred to as conductive patterns 130, separated from eachother along direction Y. Conductive patterns 130 are used forelectrically connecting semiconductor devices of cell 110 to othersemiconductor devices of cell 110 and to semiconductor devices outsideof cell 110. In some embodiments, cell 110 includes one or moreconductive patterns other than conductive patterns 130. In someembodiments, conductive patterns 130 have a rectangular shape. In someembodiments, conductive patterns 130 have a vertex (angle). Each ofconductive patterns 130 is arranged according to virtual grid lines GL.In some embodiments, center lines of conductive patterns 130 are alignedwith one of virtual grid lines GL. In some embodiments, a center line ofat least one conductive pattern 130 is offset from a correspondingvirtual grid line GL due to design variation. In some embodiments, oneor more conductive patterns 130 overlaps at least one boundary of cell110. In some embodiments, the predetermined manufacturing process is aback end of line (BEoL) process and conductive patterns 130 correspondto conductive lines or conductive vias. In some embodiments, theconductive lines in a pin layer of cell 110 serve as ports or points forconnection to elements outside of cell 110. In some embodiments, cell110 includes a multi-layer structure with a pin layer at an upper-mostlayer for connection with other cells in the same circuit block or othercells in a different circuit block. In some embodiments, the pin layerof cell 110 used for connecting is formed in metal structures close tothe gate structure. In some embodiments, the conductive patterns areformed in a second level metal (M2) layer and/or a fourth level metal(M4) layer manufacturing process. In some embodiments, the conductivepatterns are formed in a first level metal (M1) layer and a third levelmetal (M3) layer manufacturing process. In at least one embodiment, in aphysical device manufactured based on layout 200A, the conductivepatterns are formed of aluminum, copper or copper alloys, and theconductive lines are isolated by an inter-metal dielectric material. Insome embodiments, the conductive lines extend in direction Y andperpendicular to an extension of pre-layer metal lines and/or anextension of post-layer metal lines.

Returning to FIG. 2A, method 200A continues with operation 240 in whichthe at least two patterns are colored. In some embodiments, in order toenhance photolithographic resolution in the integrated circuits, amultiple exposure methodology is applied to help prevent short circuitscaused by the optical proximity effect. Patterns which are capable ofbeing decomposed for multiple exposure methodology are colorable. Insome embodiments, a double exposure involves forming patterns on asingle layer of a substrate using two different masks in succession. Asa result, a minimum line spacing in the combined pattern is reducedwhile maintaining sufficient resolution to reliably form the conductivepatterns. In a method referred to as double dipole lithography (DDL),the patterns to be formed on the layer are decomposed and formed on afirst mask having only horizontal lines, and on a second mask havingonly vertical lines. The first and second masks are said to have1-dimensional (1-D) patterns. Another form of double exposure isreferred to as double patterning technology (DPT). Unlike DDL, DPT insome cases permits a vertex to be formed of a vertical segment and ahorizontal segment on the same mask. Thus, DPT generally allows forgreater reduction in overall integrated circuit layout than DDL does.DPT is a layout splitting method analogous to a two coloring problem forlayout splitting in graph theory. Two adjacent patterns are assigneddifferent colors. Only two color types are assigned. Each pattern on thelayer is assigned to a first color or a second color. The patterns ofthe first color are formed by a first mask, and the patterns of thesecond color are formed by a second mask. In some embodiments, operation140 involves two or three different masks. In some embodiments, however,if the EDA tool is equipped with a set of default design rules withoutconsidering the optical proximity effect, operation 240 is omitted. Insome embodiments, each virtual grid line GL is assigned a specific colorduring operation 240. In the at least one embodiment in FIG. 1,conductive patterns 130 a and 130 c are assigned a first color, andconductive patterns 130 b and 130 d are assigned a second color. In someembodiments, each of conductive patterns 130 is assigned a differentcolor. Method 200A is not limited to two colors. In some embodiments,operation 240 includes assigned colors according to a triple patterningarrangement, a quadruple patterning arrangement or another suitablepatterning arrangement.

Returning to FIG. 2A, method 200A continues with operation 250 in whichan optical proximity correction (OPC) is performed. In some embodiments,a design rule check (DRC) verification is performed before the OPC.During the DRC verification, to identify whether two cells are routable,design constraints of connection between the cells are taken intoconsideration. The design constraints include limitations on speed andspacing for cells to be connected.

The OPC is applied to layout 100A to take into account photolithographicvariations/irregularities which are expected to be encountered duringmanufacturing. In some embodiments, when a width of one of conductivepatterns 130 or a distance between conductive patterns 130 is narrowerthan a predetermined lithography threshold, the OPC generates extrapolygons, such as hammerhead patterns, that are to be included in one ormore masks used to fabricate layouts 100A. After operation 250, layout100A is then used to generate one or more masks for the fabricationprocess to transfer conductive patterns 130 onto a layer of an actualwafer.

In some embodiments, additional operations are included in method 200A,such as Layout Versus Schematic (LVS) verification, Layout ParameterExtraction (LPE), and parasitic Resistance-Capacitance Extraction (RCX),or other suitable operations. In some embodiments, an order ofoperations for method 200A is modified. In some embodiments, multipleoperations for method 200A are performed simultaneously. For example,operation 240 and operation 250 are performed simultaneously, in someinstances. In some embodiments, at least one of operation 221-226 frommethod 200B is combined with an operation from method 200A.

FIG. 4 is a top view of a layout 100B of cell 110* in the integratedcircuit in accordance with some embodiments. Cell 110* is similar tocell 110, like elements have a same reference number with a star symbol.Compared with cell 110, cell 110* has an odd number of virtual gridlines GL11*-17*, collectively referred to as virtual grid lines GL*, andan even number of spacings S1112*-1617* collectively referred to asspacings S*. Similarly, a magnitude or size of each of spacing S* isarranged in a way that at least one of spacings S* is different from atleast another of spacings S*.

FIG. 5 is a top view of a layout 100C of a plurality of cells 110, 110′and 110″ in the integrated circuit in accordance with some embodiments.Cells 110′ and 110″ are similar to cell 110, like elements have a samereference number with a prime symbol or a double prime symbol. Cells110-110″ have same cell heights CH. Further, cells 110′ and 110″ areprocessed with a symmetry operation 235, respectively. Symmetryoperation 235 is referred to as a mirroring, flipping, or rotatingoperation. In cells 110 and 110′, top boundary 120T aligns with bottomboundary 120B′ to form a symmetric axis so that spacings S are symmetricto spacings S′ along direction Y. Similarly, in cells 110 and 110″,bottom boundary 120B aligns with top boundary 120T″ to form anothersymmetric axis so that spacings S are symmetric to spacings S″ alongdirection Y. Because top boundaries 120T-T″ and bottom boundaries120B-B″ align with one of the virtual grid lines, conductive patterns130 are symmetric to conductive patterns 130′ and conductive patterns130″. As a result, conductive patterns 130′ and conductive patterns 130″are assigned colors in a same way assigned to conductive patterns 130.In some embodiments, a set of different masks are made by using layoutinformation extracted from layout 100C and a photolithographic processis used to transfer the layout information from the different masks to asilicon wafer. By adjusting virtual grid lines symmetric along cellheight, method 200A and/or method 200B generates layout designs 100A-Cof integrated circuit devices with less cell displacement, higherrouting density, more uniform coloring, easier legalization (i.e., beingplaced in non-overlapping site-aligned locations) and lowermanufacturing cost of masks than other approaches.

FIG. 6 is a functional block diagram of an integrated circuit designingsystem 600 in accordance with one or more embodiments. Integratedcircuit designing system 600 includes a first computer system 610, asecond computer system 620, a networked storage device 630, and anetwork 640 connecting first computer system 610, second computer system620, and networked storage device 630. In some embodiments, one or moreof second computer system 620, networked storage device 630, and network640 are omitted.

First computer system 610 includes a hardware processor 612communicatively coupled with a non-transitory, computer readable storagemedium 614 encoded with, i.e., storing, a generated integrated layout614 a, a circuit design 614 b, and a computer program code 614 c, i.e.,a set of executable instructions. Hardware processor 612 iscommunicatively coupled to computer readable storage medium 614.Hardware processor 612 is configured to execute a set of instructions614 c encoded in computer readable storage medium 614 in order to causefirst computer system 610 to be usable as a placing and routing tool forperforming a portion or all of operations 110-150 as depicted in FIGS.1A-B. In some embodiments, hardware processor 612 is configured toexecute set of instructions 614 c for generating an integrated circuitlayout based on the layout of the cell and the minimum pitchcorresponding to a predetermined semiconductor manufacturing process. Insome embodiments, hardware processor 612 is a central processing unit(CPU), a multi-processor, a distributed processing system, anapplication specific integrated circuit (ASIC), and/or a suitableprocessing unit.

In some embodiments, computer readable storage medium 614 is anelectronic, magnetic, optical, electromagnetic, infrared, and/or asemiconductor system (or apparatus or device). In some embodiments,computer readable storage medium 614 includes a semiconductor orsolid-state memory, a magnetic tape, a removable computer diskette, arandom access memory (RAM), a read-only memory (ROM), a rigid magneticdisk, and/or an optical disk. In some embodiments using optical disks,computer readable storage medium 614 includes a compact disk-read onlymemory (CD-ROM), a compact disk-read/write (CD-R/W), and/or a digitalvideo disc (DVD).

In some embodiments, storage medium 614 stores computer program code 614c configured to cause first computer system 610 to perform method 200Aand/or method 200B as depicted in FIGS. 1A-B. In some embodiments,storage medium 614 also stores information needed for performing method200A and/or 100B or generated during performing method 200A and/or 100B,such as integrated circuit layout 614 a, circuit design 614 b, and/or acell library 614 d including layouts 200A-C of cells 210, 210*, 210′ and210″.

First computer system 610 includes an input/output interface 616 and adisplay unit 617. Input/output interface 616 is coupled to hardwareprocessor 612 and allows a circuit designer to manipulate first computersystem 610 in order to perform methods 100A-B. In at least someembodiments, display unit 617 displays the status of operation ofmethods 100A-B in a real-time manner and preferably provides a GraphicalUser Interface (GUI). In some embodiments, input/output interface 616and display unit 617 allow an operator to operate first computer system610 in an interactive manner.

In some embodiments, first computer system 610 further includes anetwork interface 618 coupled to hardware processor 612. Networkinterface 618 allows first computer system 610 to communicate withnetwork 640, to which one or more other computer systems 620 andnetworked storage device 630 are connected. Network interface 618includes wireless network interfaces such as BLUETOOTH, WIFI, WIMAX,GPRS, or WCDMA; or wired network interface such as ETHERNET, USB, orIEEE-1394. In some embodiments, method 200A and/or method 200B isimplemented in two or more computer systems 610 and 620 and/or networkedstorage device 630, and information such as integrated circuit layout614 a, circuit design 614 b, computer program code 614 c and celllibrary 614 d are exchanged between different computer systems 610 and620 and/or networked storage device 630 via network 640.

One aspect of this description relates to a method of designing alayout. The method includes identifying a cell having a cell heightbeing a non-integral multiple of a minimum pitch, generating, using aprocessor, possibilities of an ordered arrangement of a plurality ofvirtual grid lines parallel to the top boundary and the bottom boundary,and placing at least two conductive patterns on the plurality of virtualgrid lines. The cell height is defined by a top boundary and a bottomboundary, and the minimum pitch is based on a manufacturing process. Theplurality of virtual grid lines are separated from each other by aplurality of spacings, and the top boundary overlaps a first virtualgrid line of the plurality of virtual grid lines and the bottom boundaryoverlaps a second virtual grid line of the plurality of virtual gridlines. At least one spacing of the plurality of spacings is differentfrom another spacing of the plurality of spacings.

Another aspect of this description relates to a method of manufacturingan integrated circuit by a process having a minimum pitch of conductivestructures. The method includes identifying a first standard cellabutting a second standard cell along a first direction, each of thefirst standard cell and the second standard cell having a plurality ofrouting tracks extending along a second direction perpendicular to thefirst direction, forming a first set of conductive structures, by usinga first mask, on the plurality of routing tracks in the first standardcell and the second standard cell, and forming a second set ofconductive structures, by using a second mask, on the plurality ofrouting tracks in the first standard cell and the second standard cell.The first standard cell and the second standard cell have a same cellheight in the first direction, the cell height is a non-integer multipleof the minimum pitch, and a top boundary and a bottom boundary of thefirst standard cell and a top boundary and a bottom boundary of thesecond standard cell overlap the plurality of routing tracks.

Still another aspect of this description relates to an integratedcircuit designing system. The system includes a non-transitory storagemedium encoded with a set of instructions and a hardware processorcommunicatively coupled with the non-transitory storage medium andconfigured to execute the set of instructions. The set of instructionsis configured to cause the hardware processor to receive a layout of astandard cell based on a manufacturing process, the manufacturingprocess having a minimum pitch along a first direction, the standardcell having a cell height along the first direction and having aplurality of virtual grid lines perpendicular to the first direction,the cell height being a non-integral multiple of the minimum pitch. Theset of instructions is also configured to adjust the plurality ofvirtual grid lines, the plurality of virtual grid lines having at leasttwo different spacings between adjacent virtual grid lines, anarrangement of the plurality of virtual grid lines being symmetric alongthe first direction. The set of instructions is further configured toalign a plurality of patterns with the plurality of virtual grid lines.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of designing a layout, the methodcomprising: identifying a cell having a cell height being a non-integralmultiple of a minimum pitch, wherein the cell height is defined by a topboundary and a bottom boundary, and the minimum pitch is based on amanufacturing process; generating, using a processor, a set ofpossibilities of an ordered arrangement of a plurality of virtual gridlines parallel to the top boundary and the bottom boundary, wherein theplurality of virtual grid lines are separated from each other by aplurality of spacings, and the top boundary overlaps a first virtualgrid line of the plurality of virtual grid lines and the bottom boundaryoverlaps a second virtual grid line of the plurality of virtual gridlines; and placing at least two conductive patterns on the plurality ofvirtual grid lines, wherein at least one spacing of the plurality ofspacings is different from another spacing of the plurality of spacings.2. The method of claim 1, wherein generating the set of possibilities ofthe arranged of the plurality of virtual grid lines comprises: dividingthe cell height by the minimum pitch, wherein a whole number of aquotient is used to determine a quantity of spacings between adjacentvirtual grid lines; and assigning N pitch options, wherein the N pitchoptions are formed from an arithmetic sequence having a commondifference M, N being a positive integer ranging from 2 to 5, M being apositive integer equal to or greater than
 1. 3. The method of claim 2,further comprising: comparing a sum of spacings of adjacent virtual gridlines to the cell height, wherein the sum of spacings is generated fromthe N pitch options; determining whether the plurality of virtual gridlines is symmetric along the cell height; and determining whether theplurality of virtual grid lines violates a spacing design rule.
 4. Themethod of claim 3, further comprising: generating, using the processor,another set of possibilities of the ordered arrangement when the sum ofspacings of adjacent virtual grid lines is different from the cellheight, when the plurality of virtual grid lines is not symmetric alongthe cell height, or when the plurality of virtual grid lines violatesthe spacing design rule.
 5. The method of claim 1, further comprising:selecting a possibility of the generated possibilities with a largestnumber of virtual grid lines from the set of possibilities of theordered arrangement of the plurality of virtual grid lines.
 6. Themethod of claim 1, wherein the plurality of virtual grid lines isgenerated symmetric to each other about a center line of the cell,wherein the center line is parallel with the top boundary or the bottomboundary.
 7. The method of claim 1, further comprising: coloring the atleast two conductive patterns; and performing optical proximitycorrection (OPC).
 8. A method of manufacturing an integrated circuit bya process having a minimum pitch of conductive structures, comprising:identifying a first standard cell abutting a second standard cell alonga first direction, each of the first standard cell and the secondstandard cell having a plurality of routing tracks extending along asecond direction perpendicular to the first direction; forming a firstset of conductive structures, by using a first mask, on the plurality ofrouting tracks in the first standard cell and the second standard cell;and forming a second set of conductive structures, by using a secondmask, on the plurality of routing tracks in the first standard cell andthe second standard cell, wherein the first standard cell and the secondstandard cell have a same cell height in the first direction, the cellheight is a non-integer multiple of the minimum pitch, and a topboundary and a bottom boundary of the first standard cell and a topboundary and a bottom boundary of the second standard cell overlap theplurality of routing tracks.
 9. The method of claim 8, wherein theplurality of routing tracks are formed to separate from each other by aplurality of spacings, the plurality of spacings having a first spacingand a second spacing different from the first spacing.
 10. The method ofclaim 8, wherein the first standard cell is formed symmetric to thesecond standard cell along the cell height.
 11. The method of claim 8,wherein the first set of conductive structures in the first standardcell is formed symmetric to the first set of conductive structures inthe second standard cell, and the second set of conductive structures inthe first standard cell is formed symmetric to the second set ofconductive structures in the second standard cell.
 12. The method ofclaim 8, wherein a plurality of pre-layer conductive structures or aplurality of post-layer conductive structures is formed to extend alongcell height.
 13. The method of claim 8, wherein the first set ofconductive structures and the second set of conductive structures areformed by using a second metal level (M2) layer process.
 14. The methodof claim 8, wherein the first set of conductive structures and thesecond set of conductive structures are formed to have a rectangularshape or to have a vertex.
 15. An integrated circuit designing system,comprising: a non-transitory storage medium encoded with a set ofinstructions; and a hardware processor communicatively coupled with thenon-transitory storage medium and configured to execute the set ofinstructions, the set of instructions being configured to cause thehardware processor to: receive a layout of a standard cell based on amanufacturing process, the manufacturing process having a minimum pitchalong a first direction, the standard cell having a cell height alongthe first direction and having a plurality of virtual grid linesperpendicular to the first direction, the cell height being anon-integral multiple of the minimum pitch; adjust the plurality ofvirtual grid lines, the plurality of virtual grid lines having at leasttwo different spacings between adjacent virtual grid lines, anarrangement of the plurality of virtual grid lines being symmetric alongthe first direction; and place and align a plurality of patterns withthe plurality of virtual grid lines.
 16. The integrated circuitdesigning system of claim 15, when adjusting the plurality of virtualgrid lines, the set of instructions is configured to cause the processorto: divide the cell height by the minimum pitch and take a whole numberof a quotient; generate a predetermined number of pitch options based onthe whole number; and determine the plurality of spacings by thepredetermined number of pitch options.
 17. The integrated circuitdesigning system of claim 16, when determining the plurality ofspacings, the set of instructions is configured to cause the processorto: select N pitch options in an arithmetic sequence by adding minimumpitch to a common difference M, N being a positive integer from 2 to 5,M being a positive integer equal to or greater than
 1. 18. Theintegrated circuit designing system of claim 15, when adjusting theplurality of virtual grid lines, the set of instructions is configuredto cause the processor to: compare a sum of the plurality of spacings tothe cell height; determine whether the plurality of virtual grid linesis symmetric along the first direction; and determine whether theplurality of virtual grid lines violates a design rule.
 19. Theintegrated circuit designing system of claim 18, wherein the hardwareprocessing unit is configured to repetitively perform the comparingoperation and the determining operations in an iterative manner.
 20. Theintegrated circuit designing system of claim 15, wherein the set ofinstructions is configured to further cause the processor to: color theplurality of patterns; and perform an optical proximity correction (OPC)on the colored patterns.